Frozen earth storage for liquefied gas



May 17, 1966 E. E. REED FROZEN EARTH STORAGE FOR LIQUEFIED GAS Filed Oct. 16, 1964 PIT STORAGE 9 2 7 2 u U u u 2 4 u r |||1||| w n a 2 is f 5 2 P 3 4 U J 3 m 7 r\ 2 l n it W 4 T 1 2 K 4 g 3 T N 2 A A a 2 2 2 U H 3 f M s U A 8 C L I C F mm M A J F|Il llllll ll m LU A} r FL INVENTOK.

E E REED A TTORNEVS 3,251,191 FROZEN EARTH STORAGE FOR LIQUEFIED GAS Edwin E. Reed, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 16, 1964. Ser. No. 404,329 6 Claims. (Cl. 62-45) This invention relates to storage of volatile liquids in storage pits or reservoirs in frozen earth. In one of its more specific aspects the invention relates to a method and means for adding warm liquid to the frozen earth reservoir. In another of its more specific aspects it relates to a method for storing refrigeration in the frozen earth for use during filling periods so as to avoid thenecessity for mechanical refrigeration during a period when warm liquid is being added to the reservoir.

The petroleum industry produces great quantities of volatile liquid hydrocarbons as a result of processing crude oil, including natural distillate liquids, and natural gas. Volatile liquids such as propane and butane require enormous storage facilities during periods of slack use. Increased seasonal demand for such products places an increased strain on these facilities. A recent trend in the storage of volatile liquids such as propane has been to form an open-topped earthen reservoir in frozen earth and to cover the reservoir with a vapor-impermeable roof which is supported by and sealed to the frozen earth around the periphery of the reservoir. In the construction of such reservoirs it is usually the practice to drill a plurality of Well bores adjacent to and encircling the reservoir site, to case these well'bores, insert an induction United States Patent pipe into each of the cased well bores and introduce a refrigerant, such as liquid propane, through the induction pipe to near the bottom of the cased well bore and thus use these well bores as freeze pipes to freeze the earth around the reservoir site and subsequently around the reservoir itself. Liquid propane can then' be stored in the earthen reservoir at about atmospheric pressure after the roof has been installed. Vapors evolved from the stored liquid are compressed, condensed and flashed to about atmospheric pressure so as to vaporize a portion of the condensed liquid and to chill the remainder of the condensed liquid to a temperature suitable for reintroduction into the reservoir.

Refrigeration requirements for maintaining liquid propane at the required low temperature for storage at about atmospheric pressure are quite modest and therefore this method for storing volatile liquids such as propane is quite attractive and has gained considerable favor among producers and suppliers of liquefied petroleum gases (LPG).

One of the costly items which has been considered necessary in the operation of a frozen earth storage system has been the auxiliary or additional refrigeration capacity required to cool the liquefied gas that is periodically added to the reservoir. The liquefied gas to be stored in the reservoir is usually supplied by tank car or tank truck or possibly by high pressure pipe line and is received at about atmospheric temperature and a correspondingly highpressure. For example, liquid propane exerts a vapor pressure of about 185 p.s.i.a. (pounds per square inch absolute) at 100 F. Liquid propane boils at about -44 F. at atmospheric pressure and therefore the incoming liquid propane stream must be cooled to about 44 F. before it can be introduced into the reservoir. 1

According to the present invention, the incoming warm stream of liquefied gas is flashed into the flash tank which is a component of the reservoir refrigeration system to vaporize a portion of the liquid and to reduce the temperature of the remaining liquid as a result of the Jouleice Thomson effect. Chilled liquid from the flash tank is then passed into the freeze pipes adjacent the reservoir and heat is extracted from the liquid by the frozen earth surrounding the freeze pipes. The liquid, and any evolved vapors, is returned from the freeze pipes to the flash .tank to cool still further the liquid contained in the flash tank. Liquid is also passed from the freeze pipes to the reservoir by suitable control means such as a liquid level controller which controls a valve in the conduit passing from the freeze pipes to the reservoir.

Practice of the invention obviates the necessity for a separate or auxiliary refrigeration system for refrigerating the incoming warm liquid because the refrigeration system which maintains the liquid in the reservoir at the required low temperature continues to extract heat from the surrounding earth during periods when no warm liquid is being added so that the earth is always frozen in excess of that required to maintain the gas liquefied at atmospheric pressure. During periods when warm liquid is not being added to the reservoir the refrigeration system can cool the contents of the reservoir and the adjacent earth to a temperature somewhat below the normal operating temperature so as to store additional refrigeration in the frozen earth.

An object of this invention is to provide a method for reducing the amount of refrigeration needed in a frozen earth storage system. Another object of this invention is to provide an apparatus for utilizing the heat absorbing properties of frozen earth for cooling an incoming Warm liquid stream for storage in a frozen earth reservoir. Still another object of this invention is to provide a method and means for storing refrigeration in frozen earth for use in cooling a warm liquid stream that is to be added to a frozen earth reservoir. Other objects and advantages will be apparent to one skilled in the art upon reading the disclosure of this invention including the detailed description of the invention and the appended drawing.

The drawing illustrates in diagrammatic form a preferred form of apparatus for practicing my invention.

In the drawing pit storage 10 contains a supply of LPG (liquefied petroleum gas) at substantially atmospheric pressure in frozen earth. A plurality of freeze pipes comprising casings ll]l l1' and inlet pipes 12-12 surround pit storage 10. Vapors evolved from the liquid in pit storage 10 are removed via conduit 13, normally closed valve 14 and conduit 15. Valve 14 is opened by a selected pressure, e.g., 6 inches of water above atmospheric, according to a signal transmitted by pressure controller 16. Upon sensing a minimum pressure, e.g., atmospheric pressure (0 p.s.i.g.), the pressure controller 16 closes valve 14.

Vapors pass via conduit 15 to compressor 17 and then via conduit 18 and condenser 19 to accumulator 21 as liquid. Liquid is passed from accumulator 21 via conduit 22 and valve 23 to flash tank 24. Valve 23 is controlled by liquid level controller 25. Liquid is flashed to about the pit storage pressure, e.g., about atmospheric pressure, in flash tank 24 and about the temperature of the pit storage, e.g., about 44 R, for propane.

Liquid is pumped from flash tank 249 via conduit 26 and pump 27 to freeze pipes 12-12 and then via conduit 28 to flash tank 24. Liquid is also passed via valve 29 and conduit 31 to pit storage 10. Valve 29 is controlled by liquid level controller 33. Vapors from flash tank 24 pass via conduit 34, normally open valve 35 and conduit 15 to compressor 17. During normal periods of operation, when liquid is not being added to the reservoir, valves 14 and 35 will both be partially open so that vapors from the reservoir or pit storage 10 and from flash tank are compressed, condensed and returned to storage. Thus heat is continuously extracted a from the earth adjacent pit storage and the freeze pipes 1141' so as to create a reservoir for absorbing heat during a filling period. Noncondensible gases that may be introduced with fill liquid collect in the top of accumulator 21 and are Vented via conduit 32. This can be done by continuous venting through a small orifice or by manual operation of a valve at intervals.

Liquid is added to pit storage 10 via conduit 36 containing normally open valve 37, accumulator 21, conduit 22, flash tank 24, conduit 26, pump 27, freeze pipes 11 and 11, conduit 28, valve 29 and conduit 31. The liquid from the supply source, e.g., tank car or tank truck, is at about atmospheric temperature and under suilicient pressure to maintain liquid phase. The liquid in the accumulator 21 is at a similar temperature and pressure. Propane has a vapor pressure of about 185 p.s.i.a. at 100 F. and will be considered the material being stored for the purpose of description. Propane is liquid at about 44 F. at atmospheric pressure. The pressure maintained in storage pit 10 will be about 6 inches of water pressure above atmospheric pressure.

The warm liquid is flashed in flash tank 24 to vaporize a sufficient amount of the liquid to reduce the temperature of the liquid and vapor to about 44" F. In the case of propane at 100 F., about half, depending on the heat leak, will be vaporized and will be recompressed in compressor 17.

Liquid propane pumped from flash tank 24 via freeze pipes 1141 back into flash tank 24 will give up heat to the cold earth and will absorb heat in flash tank 24, thus tending to reduce the pressure in flash tank 24. If the pressure in reservoir 10 rises above a selected pressure, e.g., 8 inches of water above atmospheric pressure, controller 16 closes valve so as to increase the amount of vapor passing through conduit 13. If the pressure in flash tank 24 rises as a result of closing valve 35, pressure controller 41 closes valve 37 to stop the addition of liquid to the system. With the extra load of incoming Warm liquid removed, the refrigeration system will bring down the pressure in the reservoir lit and liquid can again be added.

In the operation of the system of this invention the valves hereinbe-fore stated to be closed will not be completely closed because the system will tend to correct the malfunction as soon as the appropriate valves begin to close. When Warm liquid is added to the system, the excess heat is absorbed by the earth adjacent the freeze pipes and since the freeze pipes usually comprise a plurality of rows or circles of pipes adjacent or encircling the freeze pit or reservoir, the capacity of the freeze pipes is usually sufficient to absorb the excess heat in any normal filling operation.

Operation of the system of the invention through a cycle of addition of warm liquid to the system and the storage of refrigeration in the earth between fill periods will now be described for the storage of liquid propane. The pressure on the storage pit will be maintained between 6 and 8 inches of water so as to prevent an undue strain on the pit roof. The maximum pressure on the flash tank is set at about 20 p.s.i.g. soas to limit the maximum temperature in the freeze pipes to about 0 F.

Fill liquid is admitted to accumulator 21 via conduit 36 and valve 37 and thence via conduit 22 and valve 23 to flash tank 24. The temperature in the accumulator 21 will be about atmospheric and the pressure will be dependent upon atmospheric temperature. Thus for an atmospheric temperature of about 80 F. the pressure in the accumulator will be about 140 p.s.i.a. or about 125 p.s.i.g. The warm liquid is flashed in flash tank 24 with the formation of a cold liquid phase and cold vapor phase. The cold liquid is passed via conduit 26, pump 27 to freeze pipes lit and 11', and then via conduit 28, valve 29 and conduit 31 to pit storage lit). At the beginning of the filling operation the pressure in the flash tank is less than atmospheric, e.g., about 10 p.s.i.a. and the temperature of the liquid being passed to storage will be about -55 to 60 F. The fill liquid will begin to give up heat to the earth around the freeze pipes and the pressure in the freeze pipes and flash tank will rise slowly as the filling progresses. The increased pressure in the freeze pipes and flash tank (and the corresponding increase in temperature) results in warmer liquid passing to storage pit It). The pressure controller 16 senses the rise in pressure in pit it) and therefore begins to open valve 14 and begins to throttle valve 35. As the filling operation continues the earth about the freeze pipes continues to warm up and if the filling operation is continued long enough the pressure in the flash tank will rise and pressure controller 4]. will begin to throttle valve 37 so as to reduce the amount of warm liquid added to the system. If the pressure in the flash tank rises to the selected maximum pressure, e.g., 20 p.s.i.g., controller 41 will close valve 37.

When the filling operation is completed pump 27 continues to pass liquid through the freeze pipes and back to the flash tank, and to the pit. The pressure in the pit is gradually lowered until pressure controller throttles valve 14 to closed or nearly closed position and valve 35 is fully open. Liquid passed via pump 27 to the freeze pipes continues to extract heat from the frozen earth until an equilibrium condition-obtains where extraction of heat is equal to the in flow of heat. This condition is maintained until another supply of warm liquid is added to storage pit 10.

That which is claimed is:

1. A method for adding from an ,external source, a V

liquefied gas at about atmospheric temperature and its vapor pressure at that temperature to a body of chilled liquefied gas at about atmospheric pressure contained in a frozen earth storage pit encircled by freeze pipes in the frozen earth, which method comprises:

flashing the added liquefied gas to about atmospheric pressure in a flash zone to vaporize a portion of the liquid so as to chill the remaining liquid to about its boiling point at about atmospheric pressure;

passing the chilled liquid to said freeze pipes in the frozen earth;

returning a first portion of liquid and any evolved vapors from said freeze pipes to said flash zone; passing a second portion of liquid from said freeze pipes to said storage pit;

compressing and condensing vapors evolved from said storage pit and said flash zone; and

flashing the condensate along with the added liquefied gas in said flash zone.

2. A method for adding from an external source a warm liquefied gas to a body of-chilled liquefied gas contained at about atmospheric pressure in a frozen earth reservoir encircled by a plurality of freeze pipes in the frozen earth, which method comprises:

flashing the warm liquefied gas to about atmospheric pressure in a flash zone to vaporize a sufficient amount of vapor to chill the remaining liquid to about its boiling point at atmospheric pressure; passing liquid from said flash zone to said freeze pipes in the frozen earth to give up heat to the frozen earth;

passing liquid from said freeze pipes to said reservoir when the liquid level in the flash zone is above a selected value; and

passing liquid from the freeze pipes to the flash zone.

3. In a system for storing chilled liquefied gas comprising a frozen earth reservoir, a' plurality of freeze pipes in the frozen earth encircling the reservoir, means to cornpress, condense and flash vapors evolved from the reservoir and flash means, the combination therewith of apparatus for chilling warm liquefied gas added from an external source to the reservoir of chilled liquefied gas comprising:

means to pass the liquid from the flash means to the freeze pipes;

means to return a first portion of liquid from said freeze pipes to said flash means and to pass a second portion of liquid from said freeze pipes to said reservoir;"'and means to sense the pressure of the flash means and to stop the addition of warm liquid when the pressure in the flash means rises to a selected value.

4. The system of claim 3 including means to sense the liquid level in the flash means and to pass liquid from the freeze pipes to the reservoir when the liquid level in the flash tank rises above a selected value.

5. The system of claim 3 including means to sense the pressure in said reservoir and to increase the pressure in the flash means when the pressure in the reservoir rises to a selected value thereby increasing the quantity of vapors withdrawn from said reservoir.

6. A system for storing a body of chilled, liquefied gas at substantially atmospheric pressure and for adding warm liquefied gas from an extraneous source to said body of chilled, liquefied gas comprising:

a reservoir in frozen earth containing a body of chilled liquefied gas at about atmospheric pressure;

a compressor;

means to pass vapor from said reservoir to said compressor;

a condenser operatively connected to said compressor to condense compressed vapor;

means to flash liquid from said condenser into said said flash tank;

a plurality of freeze pipes in the frozen earth adjacent said reservoir;

means to pass liquid from said flash tank to said freeze means to pass vapor from said flash tank to said compressor;

means to pass liquid from said freeze pipes to said reservoir;

means to pass liquid from said freeze pipes to said flash tank;

means to sense the pressure in said reservoir and to decrease the quantity of vapor passed from said flash tank to said compressor when the pressure in the reservoir exceeds a selected value; and

means to sense the pressure in said flash tank and to stop the flashing of extraneous liquid into said flash tank when the pressure in the flash tank exceeds a selected value.

References Cited by the Examiner UNITED STATES PATENTS MEYER PERLIN, Primary Examiner;

LLOYD L. KING, Examiner. 

1. A METHOD FOR ADDING FROM AN EXTERNAL SOURCE, A LIQUEFIED GAS AT ABOUT ATMOSPHERIC TEMPERATURE AND ITS VAPOR PRESSURE AT THAT TEMPERATURE TO A BODY OF CHILLED LIQUEFIED GAS AT ABOUT ATMOSPHERIC PRESSURE CONTAINED IN A FROZEN EARTH STORAGE PIT ENCIRCLED BY FREEZE PIPES IN THE FROZEN EARTH, WHICH METHOD COMPRISES: FLASHING THE ADDED LIQUEFIED GAS TO ABOUT ATMOSPHERIC PRESSURE IN A FLASH ZONE TO VAPORIZE A PORTION OF THE LIQUID SO AS TO CHILL THE REMAINING LIQUID TO ABOUT ITS BOILING POINT AT ABOUT ATMOSPHERIC PRESSURE; PASSING THE CHILLED LIQUID TO SAID FREEZE PIPES IN THE FROZEN EARTH; RETURNING A FIRST PORTION OF LIQUID AND ANY EVOLVED VAPORS FROM SAID FREEZE PIPES TO SAID FLASH ZONE; PASSING A SECOND PORTION OF LIQUID FROM SAID FREEZE PIPES TO SAID STORAGE PIT; 